The Alveolar Epithelium and Pulmonary Fibrosis

ABSTRACT

Idiopathic interstitial pneumonias (IIPs) are a heterogeneous group of diffuse pulmonary parenchymal diseases that are comprised of seven distinct clinical and pathological entities. Idiopathic pulmonary fibrosis (IPF) and cryptogenic organizing pneumonia (COP) represent two of the most prevalent members of the disease group with major differences in their pathogenesis, clinical course and prognosis. IPF is a refractory and lethal IIP characterized by fibroblast proliferation, deposition of extracellular matrix (ECM) and progressive lung scarring. The incidence of IPF is estimated at 15 to 40 cases per 100,000 per year, and the mean survival from the time of diagnosis is 3 to 5 years regardless of treatment. While its pathogenesis is incompletely understood, the currently accepted paradigm proposes that injury of the alveolar epithelium is followed by a burst of pro-inflammatory and fibroproliferative mediators that invoke responses associated with dysregulated repair of the damaged alveolar epithelium. Recently, there have been studies suggesting that the activation of the alveolar epithelial cells (AECs) may play an active role in the pathogenesis of pulmonary fibrosis. Here, we review the advances in recent studies on the role of the alveolar epithelium in pulmonary fibrosis.